This invention relates to an apparatus and a method for burning fuel. It is particularly but not exclusively concerned with the combustion of the fuel comprising a particulate carboniferous material fluidised in a gaseous carrier, particularly air.
Pulverised coal or other such particulate combustible material potentially offers a cheap source of fuel. Our co-pending application No. 82 11130 (published as U.K. patent application No. 2 099 132A) provides a method of burner for burning pulverised or particulate solid fuel employing oxygen or a gas mixture relatively rich in oxygen (typically oxygen-enriched air) to support combustion of the fuel. A typical example of the burner is shown in and described with reference to the drawings accompanying U.K. patent application No. 2 099 132A. It includes an inner passage for fuel such as pulverised coal fluidised in a carrier gas such as air, and an outer passage for substantially pure oxygen. Typically, means for forming a pilot flame are provided so as to enable the burner to be lit.
After prolonged use, burners such as that shown in a patent application No. 2 099 132A tend to fail as a result of the abrasive action of the pulverised coal wearing away the wall or walls defining the passage along which the coal is conveyed. Moreover, such erosion of the passage walls result in the formation of holes affording communication between the oxygen stream and the pulverised fuel stream. This can give rise to the formation of a potentially explosive or hazardous mixture of oxygen-enriched carrier gas and pulverised fuel. Since the outer surface of the conduit defining the passage for the pulverised fuel comes into contact with substantially pure oxygen passingthrough the outer passage it is desirable to make the conduit of a material which is safe for use with oxygen.
Copper is therefore the natural choice of material for forming this conduit. However, copper is a relatively soft metal which tends to be relatively radidly eroded by the abrasive action of the pulverised fuel, and thus a further limitation is placed on the working life of the burner.
Analogous problems may arise in the combustion of heavy fuel oil which in practice tends to have an abrasive action on the walls of the passage tha conveys it. Also, it is known to employ burners in the oxidation of chemical materials or in their thermal cracking. An example of the former process is the oxidation of ore concentrates such as copper sulphide which autogenously react (or combust) in an oxygen-rich atmosphere. The ore concentrate is conveyed through the burner in suspension in a carrier which may carry or comprise a fuel. Alternatively the fuel may be supplied separately. Sufficient oxygen is supplied for the complete combustion of the fuel and the complete oxidation of the sulphide. In this kind of example, the sulphide may cause abrasive wear of the walls of the passage that convey it through the burner. In the thermal cracking of for example sulphate waste the waste may comprise a suspension of solids in liquid or may have a fluid carried added. Again fuel may be added to the waste or may be supplied separately. The solid sulphate particles may cause abrasive wear of the walss of the passage that conveys it through the burner.